The rear wheels of a rear drive automobile are driven by a final drive unit that splits the torque received from a longitudinal propeller shaft between the two rear wheels by means of a differential gear set inside a gear housing of the final drive unit. The propeller shaft drives an internal pinion gear that drives an internal ring gear attached to a rotary differential case. The differential case supports equalizing gears that drive two side gears that are attached to drive shafts that are connected to the respective rear wheels.
The bottom of the gear housing is a reservoir that is filled with lubricant that is distributed to the various differential gears during operation of the final drive unit. This lubricant can become quite hot. Consequently, a final drive unit often has lubricant cooling provisions.
European Patent Application 0 067 639 published Dec. 22, 1982 discloses an axle that includes a final drive unit that has a gear housing and a removable cover member. The cover member and an intermediate member provide an internal chamber that has an opening at the top. Lubricant is thrown into the internal chamber through the top opening by the rotating ring gear during operation of the final drive unit. The internal chamber also has an opening at the bottom of the intermediate member that is sufficiently small so that the chamber remains substantially full of lubricant during operation of the final drive unit. Cooling of the lubricant is facilitated by heat conduction through the wall of the removable cover member. The wall may be provided with cooling fins.